| Re: match_2d [message #66183] |
Thu, 23 April 2009 05:10  |
vino
Messages: 36
Registered: March 2008
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Member |
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Hi Jeremy!!
Thank you very much for helping me out....It works very well with my
data set...
For me to be able to use this routine is going to save me about a
couple of weeks of runtime in my program!!
I have looked at WITHINSPHRAD but in that case, i still need to have
a loop which is what i was trying to avoid!!
Thanks to J.D.Smith for giving us a boon with routines like this!! ( i
will someday learn how to use histogram)..
Regards,
Vino
On Apr 22, 11:39 pm, JDS <jdtsmith.nos...@yahoo.com> wrote:
>> Aha... I've looked at it in gory detail, and it turns out that the
>> routine implicitly assumes that the minimum value of both x2 and y2
>> are 0. So you can get it to work if you do the following:
>
> Aha! Thanks for the catch. That's what you get when you evaluate an
> algorithm on artificial random coordinates ranging uniformly from
> [0,1].
>
> I've updated MATCH_2D at the address mentioned to handle this issue
> explicitly, and also catch cases of matching points which fall just
> slightly outside the bounding box of the search set. I've also added
> a much-needed warning regarding using this Euclidean matching
> algorithm for points on the sphere (e.g. star positions, lat/lon,
> etc.):
>
> ; WARNING:
> ;
> ; Distance is evaluated in a strict Euclidean sense. For
> ; points on a sphere, the distance between two given
> ; coordinates is *not* the Euclidean distance. As an extreme
> ; example, consider two points very near the N. pole, but on
> ; opposite sides (one due E, one due W). For small patches,
> ; this Euclidean assumption is approximately valid, and the
> ; method works. See NOTES above for a tip regarding obtaining
> ; a (more) uniform match criterion on the sphere.
> ;;
>
> Give this version a try. By the way, the value of MATCH_DISTANCE for
> points which did *not* match is not meaningful.
>
> JD
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